Thin film transistor with multiple gates using super grain silicon crystallization

ABSTRACT

A thin film transistor with multiple gates using a SGS process which is capable of materializing multiple gates without increasing dimensions and a method thereof. The thin film transistor has a thin film transistor using super grain silicon (SGS) crystallization comprising a semiconductor layer formed on an insulating substrate in a zigzag shape, and a gate electrode formed so that it intersects with the semiconductor layer, wherein the semiconductor layer gas a high-angle grain boundary at apart which does not cross the gate electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of application Ser. No. 10/890,999, filed Jul. 15, 2004, which is a divisional application of application Ser. No. 10/298,559. This application also claims the benefit of Korean Application No. 2001-81446, filed Dec. 19, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin film transistor using super grain silicon crystallization (hereinafter referred to as “SGS”), and more particularly, to a TFT with multiple gates which prevents defects by removing a high-angle grain boundary in a channel region and reduces leakage current by materializing multiple gates without increasing the area.

2. Description of Related Art

A polysilicon film which is used as a semiconductor layer of a TFT is formed by crystallizing the deposited amorphous silicon film after depositing an amorphous silicon film on a substrate. Methods of crystallizing the amorphous silicon film into a polysilicon film include solid phase crystallization (SPC), eximer laser annealing (ELA), metal induced lateral crystallization (MILC), etc. The SPC process has problems of a high crystallization temperature and a long period of process time while the ELA process has problems of time and space non-uniformities due to instability of a laser. Although the MILC process has merits of a relatively low process temperature and short process time using ordinary heat treatment equipment, it has problems in that a leakage current of a device fabricated by the MILC process is larger than that of a device fabricated by other crystallization methods.

A method of fabricating a TFT using the MILC process is disclosed in U.S. Pat. No. 5,773,327. The method of fabricating a TFT suggested in U.S. Pat. No. 5,773,327 requires an additional mask process to form an MILC region, and the existence of MILC surfaces in the channel region act as defects of the TFT. The MILC surface refers to a portion in which two surfaces of crystallized polysilicon grown in an opposite direction by the MILC technique meet.

On the other hand, there are problems in that a crystallization time is increased since dimensions by multiple gates are increased, and dimensions separated between metal layers of the MILC are increased in the case that multiple gates are applied to control leakage current.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a TFT which is capable of realizing multiple gates without increasing dimensions thereof, and a method of fabricating the same.

It is another object of the present invention to provide a TFT with multiple gates which are capable of reducing leakage current, and a method of fabricating the same.

It is another object of the present invention to provide a TFT with multiple gates using each of separated multi-channel layers, and a method of fabricating the same.

It is another object of the present invention to provide a TFT with multiple gates using a SGS process in which a high angle-grain boundary exists outside a channel layer, and a method of fabricating the same.

It is another object of the present invention to provide a method of fabricating a TFT with multiple gates using a SGS process which is capable of reducing the masking process.

Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

The foregoing and other objects of the present invention may be achieved by providing a thin film transistor using super grain silicon (SGS) crystallization comprising: a semiconductor layer formed on an insulating substrate in a zigzag shape; and a gate electrode formed so that it intersects with the semiconductor layer, wherein the semiconductor layer gas a high-angle grain boundary at apart which does not cross the gate electrode.

The semiconductor layer comprises: two or more body parts intersecting with the gate electrode; and one or more connection parts to connect each neighboring body part, and wherein a part intersecting with the gate electrode in the semiconductor layer acts as a channel region.

The gate electrode is equipped with one or more slots intersecting the semiconductor layer, wherein a part overlapped with the channel region of the semiconductor layer acts as a multiple gate.

The foregoing and other objects of the present invention may also be achieved by providing a thin film transistor, comprising: multi-semiconductor layers each of which are adjacently formed on an insulating substrate; and a gate electrode which is formed so that it intersects with the semiconductor layer, wherein a high-angle grain boundary do not exist in the multi-semiconductor layers.

The foregoing and other objects of the present invention may also be achieved by providing a thin film transistor, comprising: multi-semiconductor layers each of which are adjacently formed on an insulating substrate; and a gate electrode which is formed so that it intersects with the semiconductor layer, thereby forming different channel regions, wherein a high-angle grain boundary do not exist in the channel regions.

The foregoing and other objects of the present invention may also be achieved by providing a thin film transistor comprising: a semiconductor layer formed in a rectangular shape having one side open or formed in a zigzag shape on an insulating substrate; and a gate electrode having at least one slot crossing the semiconductor layer; wherein the semiconductor layer has a high-angle grain boundary at a part corresponding to the slot of the gate electrode; wherein the semiconductor layer comprises: two or more body parts intersecting with the gate electrode, and one or more connection parts to connect the neighboring body parts, wherein channel regions are formed where the body parts intersect with the gate electrode; and wherein multiple gates are formed on the gate electrode, corresponding to the channel regions formed on the semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1A to FIG. 1D are sectional views illustrating a method of fabricating a multi-gate TFT using a SGS process according to an embodiment of the present invention.

FIG. 2A to FIG. 2D are plan views illustrating a method of fabricating a multi-gate TFT using the SGS process according to the embodiment of FIGS. 1A to 1D.

FIG. 3A to FIG. 3F are sectional views illustrating a method of fabricating a multi-gate TFT using a SGS process according to another embodiment of the present invention.

FIG. 4A to FIG. 4F are plan views illustrating a method of fabricating a multi-gate TFT using the SGS process according the embodiment of FIGS. 3A to 3D.

FIG. 5A to FIG. 5D are process sectional views illustrating a method of fabricating a 4-fold gate TFT using the SGS process according to yet another embodiment of the present invention.

FIG. 6A to FIG. 6D are plan views illustrating a method of fabricating a 4-fold gate TFT using the SGS process according to the embodiment of FIGS. 5A to 5D.

FIG. 7 is a drawing illustrating a structure of the multiple gates in a TFT with multiple gates using the SGS process according to yet another embodiment of the present invention.

FIG. 8A to FIG. 8C are plan views illustrating a method of fabricating a TFT with multiple gates using a SGS process according to yet another embodiment of the present invention.

FIG. 9A to FIG. 9C are plan views illustrating a method of fabricating a TFT with multiple gates using a SGS process according to yet another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.

FIG. 1A to FIG. ID are sectional views illustrating a method of fabricating a multi-gate TFT using a SGS process according to an embodiment of the present invention, and FIG. 2A to FIG. 2D are plan views illustrating a method of fabricating a multi-gate TFT using the SGS process according to the embodiment of FIG. 1A to FIG. 1D, wherein FIG. IA to FIG. 1D are the cross-sectional structures illustrating a fabrication method according to a line 1A-1A′ of FIG. 2D.

Referring to FIG. 1A and FIG. 2A, a buffer layer 11 is formed on a insulating substrate 10 such as a glass substrate, and an amorphous silicon film is patterned using a first mask (which is not shown in the drawings) after depositing an amorphous silicon film on the buffer layer 11 so that a semiconductor layer 12 a having an amorphous silicon film is formed, wherein the semiconductor layer 12 a comprising an amorphous silicon film has a “

” shaped structure equipped with body parts 12L1 and 12L2 and a connection part 12B connecting the body parts 12L1 and 12L2.

Although several embodiments of the present invention exemplify that the semiconductor layer 12 a has a “

” shaped structure equipped with a pair of body parts 12L1 and 12L2 and a connection part 12B connecting the body parts 12L1 and 12L2, the semiconductor layer 12 a is not necessarily limited to such a structure, but can have a “

” or “

” shaped structure, or a combination thereof equipped with a plurality of body parts 12L, wherein each of the plurality of body parts 12L are connected by a plurality of connection parts 12B so that the semiconductor layer 12 a has a zigzag shaped structure.

Referring to FIG. 1B and FIG. 2B, a gate electrode material is deposited on the gate insulating film 14 after forming a gate insulating film 14 on a buffer layer 11 comprising the semiconductor layer 12 a. A gate electrode 16 is formed by patterning the gate electrode material using a second mask (which is not shown on the drawings).

The gate electrode 16 is formed so that it intersects with the body parts 12L1 and 12L2 of the semiconductor layer 12 a, wherein a part 16-1 of the gate electrode 16 overlapping a first body part 12L1 acts as a first gate while a part 16-2 overlapping a second body 12L2 acts as a second gate, thereby obtaining a multi-gate.

On the other hand, the gate electrode 16 has a structure of multiple gates since parts overlapping each of the body parts 12L act as a gate where the semiconductor layer 12 a is not formed in a “

” shape, but formed in a zigzag shape equipped with a plurality of body parts 12L.

Impurity areas 12-11˜12-13 for source/drain regions are formed by ion-implanting impurities, for example, N-type or P-type impurities into the semiconductor layer 12 a comprising an amorphous silicon film after forming the gate electrode 16.

A part of the lower part of the first gate 16-1 in the semiconductor layer 12 a comprises an amorphous silicon film, namely, a part between impurity areas 12-11 and 12-12 for source/drain regions acts as a first channel region 12-21, and a part of the lower part of the second gate 16-2, namely, a part between impurity areas 12-12 and 12-13 for the source/drain regions acts as a second channel region 12-22.

Referring to FIG. 1C, FIG. 1C′ and FIG. 2C, an interlayer insulating film 18 is formed on the gate insulating film 14 comprising the gate electrode 16, and contact holes 19-1 and 19-2 are respectively formed in impurity areas 12-11 and 12-13 for the source/drain regions by etching the interlayer insulating film 18 and the gate insulating film 14 using a third mask (which is not shown on the drawings). The contact holes 19-1 and 19-2 are formed at edge parts of both sides of a zigzag shaped semiconductor layer 12a so that the contact holes 19-1 and 19-2 are formed at one side edge of the body part arranged at the outermost wall part in a plurality of body parts 12L1 and 12L2, that is, one side edge of the body part that is not connected by a connection part 12B.

Subsequently, referring to FIG. 1C, a capping layer 20 and a metal film 21 are formed each to a thickness of several to hundreds of angstroms Å. The capping layer 20 is formed so that the capping layer 20 directly contacts exposed impurity areas 12-11 and 12-13 in the semiconductor layer 12 a comprising the amorphous silicon film through the contact holes 19-1 and 19-2. The capping layer 20 controls a diffused metal concentration from the metal film 21 to the amorphous silicon film. The capping layer 20 is made of SiO2 or SiNx, preferably made of SiO2. The metal film 21 is diffused into the amorphous silicon film and can form crystallization seeds such as Ni or Pd on the front surface of a substrate.

On the other hand, referring to FIG. 1C′, instead of forming the capping layer 20, the gate insulating film 14 remains in the source/drain regions. The remaining gate insulating film 14 in the source/drain regions act as the capping layer when SGS process proceeds.

Referring to FIG. 1D and FIG. 2D, a semiconductor layer 12 comprises a polycrystalline silicon film formed by crystallizing an amorphous silicon film 12 a using a SGS process, wherein a high-angle grain boundary 12-3 does not exist in first and second channel regions 12-21 and 12-22 of the semiconductor layer 12, but exists in an impurity area 12-12 for the source/drain regions. The high-angle grain boundary means that grown grains are met, thereby forming a grain boundary.

And then, the capping layer 20 and/or the metal film 21 is(are) removed.

Subsequently, source/drain electrodes 22-1 and 22-2 are formed by patterning the metal for the source/drain electrodes 21 using a fourth mask (which is not shown on the drawings) after depositing metal for source/drain electrodes 21.

FIG. 3A to FIG. 3F illustrate process sectional views illustrating a method of fabricating a multiple gate TFT with a multi-semiconductor layer using a SGS process according to another embodiment of the present invention, and FIG. 4A to FIG. 4F illustrate plan views illustrating a method of fabricating a multiple gate TFT with a multi-semiconductor layer using the SGS process according to the embodiment of FIG. 3A to FIG. 3F, wherein FIG. 3A to FIG. 3F illustrate the cross-sectional structure according to a line 3A-3A′ of FIG. 4F limited to a first semiconductor layer in the multi- semiconductor layer, and a second semiconductor layer has the same structure as the first semiconductor layer.

Referring to FIG. 3A and FIG. 4A, a buffer layer 31 comprising an oxidation film is formed on an insulating substrate 30 such as a glass substrate, and an amorphous silicon film 32 and an oxidation film as a blocking layer 33 are subsequently formed on a buffer layer 31.

A photosensitive film 34 having the same pattern as a mask to form a multi-semiconductor layer formed in the subsequent process is formed on the blocking layer 33 using a first mask (which is not shown on the drawings), wherein the photosensitive film 34 has a first pattern 34-1 for a first semiconductor layer and a second pattern 34-2 for a second semiconductor layer which are spaced apart from each other by a predetermined distance.

A first pattern 33-1 functioning as a blocking layer for the first semiconductor layer and a second pattern 33-2 functioning as a blocking layer for the second semiconductor layer are formed by patterning the blocking layer 33 at the lower part of the photosensitive film 34 using the photosensitive film 34.

Referring to FIG. 3B and FIG. 4B, when the photosensitive film 34 is applied so as to completely cover the patterned blocking layer 33, a first pattern 34-1 a and a second pattern 34-2 a of a photosensitive film 34 a contact each other, and the blocking layer 33 and an amorphous silicon film 32 between the first pattern 34-1 a and the second pattern 34-2 a are completely covered by the photosensitive film 34 a.

Subsequently, referring to FIGS. 3C and 4C, a capping layer 35 and a metal film 36 are formed each to a thickness of several to hundreds of angstroms A. The capping layer 35 controls a diffused metal concentration from the metal film 36 to the amorphous silicon film. The capping layer 35 is made of SiO2 or SiNx, preferably made of SiO2. The metal film 36 is diffused into the amorphous silicon film and can form crystallization seeds such as Ni or Pd on the front surface of a substrate.

The blocking layer 33 is exposed by removing the photosensitive film 34 a.

Referring to FIG. 3D and FIG. 4D, a polycrystalline silicon film 32 a is formed by crystallizing the amorphous silicon film 32 using the SGS process, and then the remaining a capping layer 35 and metal film 36 are removed, wherein the polycrystalline silicon film 32 a is divided into a part crystallized by the SGS portion 32 a-2 without the crystallization seeds and a part crystallized by the SGS portion 32 a-1 portion with the crystallization seeds, and a high-angle grain boundary 32-5 is also exposed by existing between a first pattern 33-1 and a second pattern 33-2 of the neighboring blocking layer 33.

Referring to FIG. 3E and FIG. 4E, a multi-semiconductor layer comprising a first semiconductor layer 40 a and a second semiconductor layer 40 b including only a part crystallized by the SGS process is formed by etching the polycrystalline silicon film 32 a at the lower part of the blocking layer 33 using the first pattern 33-1 and the second pattern 33-2 of the blocking layer 33 as a mask, wherein the exposed high-angle grain boundary 32-5 is removed and does 20 not exist in the first and second semiconductor layers 40 a and 40 b when forming the first semiconductor layer 40 a and the second semiconductor layer 40 b using the blocking layer 33 as a mask.

Subsequently, a gate insulating film 37 is formed on the front surface of a substrate after removing the blocking layer 33, and a gate electrode 38 is formed on the gate insulating film 37 using a second mask (which is not shown in the drawings) to form a gate, wherein a part overlapped by the first semiconductor layer 40 a acts as a first gate 38-1, and a part overlapped by the second semiconductor layer 40 b acts as a second gate 38-2 in the gate electrode 38.

Each of impurity areas 39 a-39 d for source/drain regions are formed by ion-implanting high concentrated impurities of P-type or N-type into the first semiconductor layer 40 a and the second semiconductor layer 40 b using the gate electrode 38 as a mask, wherein a part overlapped by the first gate 38-1 in the first semiconductor layer 40 a acts as a first channel region while a part overlapped by the second gate 38-2 in the second semiconductor layer 40 b acts as a second channel region.

Referring to FIG. 3F and FIG. 4F, an interlayer insulating film 41 is formed on the front surface of the substrate, and contacts 41 a and 41 b for the source/drain electrodes 42 a and 42 b and linking contacts 41 c and 41 d to connect first and second semiconductor layers 40 a and 40 b, that is, impurity areas 39 b and 39 d for source/drain regions are formed by etching the interlayer insulating film 41 and the gate insulating film 37 so that the impurity areas 39 a through 39 d are exposed using a third mask (which is not shown in the drawings) to form contacts.

Source/drain electrodes 42 a and 42 b connected with impurity areas 39 a and 39 c for the source/drain regions through contacts 41 a and 41 b, a link 42 c, and a data line 42 d to connect impurity areas 39 b and 39 d for the source/drain regions through linking contacts 41 c and 41 d are formed by patterning the deposited electrode material using a fourth mask (which is not shown in the drawings) to form the source/drain electrodes after depositing a source/drain electrode material on the interlayer insulating film 41.

The method of fabricating a thin film transistor according to this embodiment enables fabricating of a multi-gate thin film transistor using the SGS technique without an additional masking process, thereby not only simplifying the processes involved, but also suppressing leaking of current by removing the high-angle grain boundary containing a large amount of metal during the etching process to form a multi-semiconductor layer, thus removing the causes of defects.

Furthermore, although it is illustrated in this embodiment that the gate has an “I” shaped structure, it is also possible that the gate can be formed as a structure having a plurality of slots as described in the following examples. In this case, a thin film transistor not having a multi-gate structure of a multi-semiconductor layer but having a structure of 2×N (slot numbers of the gate electrode+1) multi-channel layers or multiple gates is supplied instead.

FIG. 5A to FIG. 5D are sectional views illustrating a method of fabricating a TFT with 4-fold gates using a SGS process according to another embodiment of the present invention, and FIG. 6A to FIG. 6D illustrate plan views of a method of fabricating a TFT with 4-fold gates using the SGS process according to the embodiment of FIGS. 5A to 5D, wherein the process sectional views of FIG. 5A to FIG. 5D illustrate the cross-sectional structure according to line 5A-5A′ of FIG. 6D.

Referring to FIG. 5A and FIG. 6A, a buffer layer 51 is formed on an insulating substrate 50 such as a glass substrate, and an amorphous silicon film is deposited on the buffer layer 51. A semiconductor layer 52 a comprising an amorphous silicon film is formed by patterning the amorphous silicon film using a first mask (which is not shown in the drawings). The semiconductor layer 52 a comprising an amorphous silicon film has a “

” shaped structure equipped with body parts 52L1 and 52L2 and a connection part 52B to connect the body parts 52L1 and 52L2.

Although a “

” shaped structure is illustrated in the drawings in which the semiconductor layer 52 a is equipped with a pair of body parts 52L1 and 52L2 and a connection part 52B to connect the body parts 52L1 and 52L2, the semiconductor layer 52 a is not limited to the body parts 52L1 and 52L2 and the connection part 52B, but can be equipped with a plurality of body parts 52L, wherein the plurality of body parts 52L are connected by a plurality of connection parts 52B respectively so that the semiconductor layer 52 a has a zigzag shaped structure.

Referring to FIG. 5B and FIG. 6B, a gate electrode material is deposited on a gate insulating film 54 after forming a gate insulating film 54 on a buffer layer 51 including the semiconductor layer 52 a comprising an amorphous silicon film. A gate electrode 56 is formed by patterning the gate electrode material using a second mask (which is not shown in the drawings).

The gate electrode 56 is formed so that it intersects with body parts 52L1 and 52L2 of the semiconductor layer 52 a, wherein the gate electrode 56 is equipped with one slot 56S crossing the body parts 52L1 and 52L2, thus equipped with 4-fold gates. That is, in the gate electrode 56, parts 56-1 and 56-2 overlapping a first body part 52L1 out of the body parts 52L1 and 52L2 act as first and second gates, and parts 56-3 and 56-4 overlapping a second body part 52L2 out of the body parts 52L1 and 52L2 act as third and fourth gates.

Impurity areas 52-11 through 52-15 for source/drain regions are formed by ion-planting impurities, for example, N-type or P-type impurities into a semiconductor layer 52 a comprising an amorphous silicon film after forming the gate electrode 56.

In the semiconductor layer 52 a comprising an amorphous silicon film, a part of the lower part of the first gate 56-1, namely, a part between impurity areas 52-11 and 52-12 for source/drain regions acts as a first channel region 52-21, and a part of the lower part of the second gate 56-2, namely, a part between impurity areas 52-12 and 52-13 for source/drain regions acts as a second channel region 52-22.

Furthermore, in the semiconductor layer 52 a comprising an amorphous silicon film, a part of the lower part of the third gate 56-3, namely, a part between impurity areas 52-13 and 52-14 for source/drain regions acts as a third channel region 52-23, and a part of the lower part of the fourth gate 56-4, namely, a part between impurity areas 52-14 and 52-15 for source/drain regions acts as a fourth channel region 52-24.

On the other hand, the gate electrode 16 may act as a multiple gate structure where a part overlapping each of the body parts 52L acts as a gate when the semiconductor layer 52 a has a zigzag shape equipped with a plurality of body parts 52L.

Referring to FIG. 5C and FIG. 6C, an interlayer insulating film 58 is formed on a gate insulating film 54 comprising the gate electrode 56, and contact holes 59-1 through 59-3 are formed so that the impurity areas 52-11, 52-13 and 52-15 for source/drain regions are exposed by etching the interlayer insulating film 58 and the gate insulating film 54 using a third mask (which is not shown in the drawings).

Subsequently, a capping layer 60 and a metal film 61 are formed each to a thickness of several to hundreds of angstroms Å. The capping layer 60 is formed so that the capping layer 60 directly contacts exposed impurity areas 52-11 and 52-15 exposed through first and second contact holes 59-1 and 59-2 and directly contacts exposed impurity areas 52-13 exposed through a third contact hole 59-3.

The capping layer 60 controls a diffused metal concentration from the metal film 61 to the amorphous silicon film. The capping layer 60 is made of SiO2 or SiNx, preferably made of SiO2. The metal film 61 is diffused into the amorphous silicon film and can form crystallization seeds such as Ni or Pd on the front surface of a substrate.

On the other hand, referring to FIG. 5C′, instead of forming the capping layer 60, the gate insulating film 54 remains in the source/drain regions. The remaining gate insulating film 54 in the source/drain regions act as the capping layer 60 when SGS process proceeds.

Referring to FIG. 5D and FIG. 6D, a semiconductor layer 52 comprising a polycrystalline silicon film is formed by crystallizing an amorphous silicon film 52 a using the SGS process. A crystallization time is further shortened since crystallization is simultaneously progressed at both sides of the body parts differently than in the embodiment of FIGS. 1A to 1D during the crystallization using the SGS process. Therefore, a high-angle grain boundary does not exist in first to fourth channel regions 52-21 through 52-24, but exists between the slots 56S of the gate electrode 56, namely, in the impurity areas 52-12 and 52-14 for the source/drain regions.

A high-angle grain boundary which is not in the channel regions exists in the impurity area 52-13 where the crystallization process is preceded in the same method as in the embodiment of FIGS. 1A to 1D.

And then, the capping layer 60 and/or the metal film 61 is(are) removed.

Subsequently, the source/drain electrodes 62-1 and 62-2 are formed, and a conductive pattern 62-3 contacting the impurity area 52-13 through the third contact hole 59-3 is formed by patterning the metal material for source/drain electrodes using a fourth mask (which is not shown in the drawings) after depositing a metal for source/drain electrodes.

FIG. 7 illustrates the plan structure of a thin film transistor with multiple gates according to another embodiment of the present invention.

Referring to FIG. 7, a semiconductor layer 72 has a zigzag shape equipped with a plurality of connection parts 72B to connect a plurality of body parts 72L1 and 72L2 with each neighboring body parts 72L1 and 72L2, and a gate electrode 76 is equipped with a plurality of slots, for example, 76S1 through 76S3 which are formed so as to intersect with the semiconductor layer 72.

A thin film transistor according to this embodiment can be fabricated by the same method as in the previous embodiments, wherein the case that the MILC process is progressed in one direction only as in FIGS. 1A to 1D is not influenced by the number of slots since a high-angle grain boundary is formed at the connection part.

However, it is preferable to form slots at the central part of the body in which a high-angle grain boundary is to exist since the high-angle grain boundary exists in the body part where the SGS process is progressed in both directions as in FIGS. 5A to 5D, and it is particularly preferable that the number of slots is an odd number so that the high-angle grain boundary does not exist in channel regions, but rather in a semiconductor layer in the slots. The reason that the high-angle grain boundary does not exist in the channel regions, but in the semiconductor layer in the slots positioned at the center is that the number of slots is an odd number while the high-angle grain boundary does exist in the channel regions in the semiconductor layer in case that the number of the slots is an even number.

A separate masking process to form a metal film for the SGS process and a process to remove the metal film remaining after the SGS process is excluded so that the processes of forming a TFT with multiple gates are simplified, and a high-angle grain boundary does not exist in the channel regions so as to prevent generation of defects and reduce leakage current in methods of fabricating a thin film transistor with multiple gates according to the embodiments of FIGS. 1A to 1D, 5A to 5D, and FIG. 7. Furthermore, the thin film transistors with multiple gates are fabricated by forming the semiconductor layers and the gate electrodes so that zigzag shaped semiconductor layers intersect with gate electrodes, thereby reducing leakage current without increasing the dimensions as.

Furthermore, multiple gates having the number of M (number of body parts of a semiconductor layer)×N (number of slots of a gate electrode+1) are realized by forming the semiconductor layer in a zigzag shape and forming a gate electrode equipped with one or more slots crossing the semiconductor layer in the methods of fabricating a thin film transistor with multiple gates according to the embodiments of FIGS. 1A to 1D, FIGS. 5A to 5D and FIG. 7 of the present invention.

FIG. 8A to FIG. 8C are plan views illustrating a method of fabricating a TFT with multiple gates using the SGS process according to another embodiment of the present invention.

A semiconductor layer is formed by patterning the polycrystalline silicon film after crystallizing an amorphous silicon film into a polycrystalline silicon film using an SGS process in a method of fabricating a thin film transistor with multiple gates according to the embodiment of FIGS. 8A to 8C.

That is, the amorphous silicon film 82 a is crystallized into a polycrystalline silicon film 82 b by depositing an amorphous silicon film 82 a on an insulating substrate 80 comprising a buffer layer (which is not shown in the drawing), forming a capping layer 83 for a diffusing controlling layer and a metal film 84 for a catalyst layer of the SGS at both edge parts as illustrated in FIG. 8A, and progressing the SGS process as illustrated in FIG. 8B.

Subsequently, a “

” shaped semiconductor layer 82 is formed by patterning the polycrystalline silicon film 82 b using a mask for the semiconductor layer after removing the capping layer 83 and the metal film 84, as illustrated in FIG. 8C. This embodiment can be applied to a thin film transistor having the same structure as in the embodiment of FIGS. 1A to 1D so that a high-angle grain boundary 82 c exists outside channel regions. Thereafter, a thin film transistor with multiple gates is fabricated by the same method as in the embodiment of FIGS. 1A to 1D.

FIG. 9A to FIG. 9C are plan views illustrating a method of fabricating a TFT with multiple gates using a SGS process according to another embodiment of the present invention.

In this embodiment, a semiconductor layer is formed by patterning the polycrystalline silicon film after crystallizing an amorphous silicon film into a polycrystalline silicon film using the SGS process as in the embodiment of FIGS. 8A to 8C.

That is, the amorphous silicon film 92 a is crystallized into a polycrystalline silicon film 92 b by depositing an amorphous silicon film 92 a on an insulating substrate 90, forming a capping layer 93 for a diffusing controlling layer and a metal film 94 of the SGS at both edge parts, as illustrated in FIG. 9A, and progressing the SGS process, as illustrated in FIG. 9B.

Subsequently, a “

” shaped semiconductor layer 92 is formed by patterning the polycrystalline silicon film 92 b using a mask for the semiconductor layer after removing the capping layer 93 and the metal film 94, as illustrated in FIG. 9C. This embodiment can be applied to a thin film transistor having the same structure as in the embodiment of FIG. 7 so that a high-angle grain boundary 92 c exists outside channel regions during formation of multiple gates. Thereafter, a thin film transistor with multiple gates is fabricated in the same method as in the previous embodiment.

As described above, a method of fabricating a thin film transistor with multiple gates using the SGS process has merits in that a separate masking process of forming a capping layer and a metal film for the SGS and a process of removing the capping layer and the metal film after the SGS is removed so as to simplify the processes, and a high-angle grain boundary does not exist in channel regions so as to reduce leakage current.

The thin film transistors according to the embodiments of the present invention have merits in that multiple gates having the number of M (number of body parts of a semiconductor layer)×N (number slots of a gate electrode+1) are realized without increasing dimensions by forming the semiconductor layer in a zigzag shape and forming a gate electrode equipped with one or more slots crossing the semiconductor layer.

Furthermore, the present invention not only reduces leakage current and manufacturing cost but also shortens process time by forming a thin film transistor with multiple gates using the SGS process without an additional masking process.

Furthermore, the present invention enables compact designs since dimensions are not increased by forming a semiconductor layer in a zigzag shape and forming a plurality of slots on gate electrodes so that the slots intersect with the semiconductor layer, thereby forming a thin film transistor with multiple gates. Therefore, the present invention has merits in that leakage current is suppressed, and reliability is improved with an opening ratio not being influenced to a large extent.

Although a few embodiments of the present invention have been shown and described, it would be appricaiated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equvalents. 

1. A thin film transistor comprising: a semiconductor layer formed on an insulating substrate in a zigzag shape; and a gate electrode formed so that it intersects with the semiconductor layer, wherein the semiconductor layer gas a high-angle grain boundary at apart which does not cross the gate electrode.
 2. The thin film transistor of claim 1, wherein the semiconductor layer comprises: two or more body parts intersecting with the gate electrode; and one or more connection parts to connect each neighboring body parts, and wherein a part intersecting with the gate electrode in the semiconductor layer acts as a channel region and a part overlapped by the channel region of the semiconductor layer acts as a multiple gate.
 3. The thin film transistor of claim 2, wherein the semiconductor layer has the high-angle grain boundary at the connection parts.
 4. The thin film transistor of claim 1, wherein the gate electrode is equipped with one or more slots intersecting with the semiconductor layer.
 5. The thin film transistor of claim 4, wherein the semiconductor layer has the high-angle grain boundary at parts corresponding to the slots of the gate electrode.
 6. The thin film transistor of claim 1, wherein the semiconductor layer is formed in a C shape.
 7. The thin film transistor of claim 1, wherein the semiconductor layer is formed in an E shape.
 8. A thin film transistor comprising: multi-semiconductor layers each of which are adjacently formed on an insulating substrate; and a gate electrode which is formed so that it intersects with the semiconductor layer, wherein a high-angle grain boundary do not exist in the multi-semiconductor layers.
 9. The thin film transistor of claim 8, wherein the semiconductor layer comprises two or more body parts intersecting with the gate electrode; and one or more connection parts to connect each neighboring body parts, and wherein a part intersecting with the gate electrode in the semiconductor layer acts the channel region and a part overlapped with the channel region of the semiconductor layer acts a multiple gate.
 10. The thin film transistor of claim 9, wherein the semiconductor layer has a high-angle grain boundary at the connection parts.
 11. The thin film transistor of claim of claim 8, wherein the gate electrode is equipped with one or more slots intersecting with the semiconductor layer.
 12. The thin film transistor of claim 11, wherein the semiconductor layer has the high-angle grain boundary at parts corresponding to the slots of the gate electrode.
 13. The thin film transistor of claim 9, wherein the connection parts are different layers from the semiconductor layers.
 14. A thin film transistor, comprising: multi-semiconductor layers each of which are adjacently formed on an insulating substrate; and a gate electrode which is formed so that it intersects with the semiconductor layer, thereby forming different channel regions, wherein a high-angle grain boundary do not exist in the channel regions.
 15. The thin film transistor of claim 14, wherein the semiconductor layer comprises two or more body parts intersecting with the gate electrode; and one or more connection parts to connect each neighboring body parts, and wherein a part intersecting with the gate electrode in the semiconductor layer acts the channel region and a part overlapped with the channel region of the semiconductor layer acts a multiple gate.
 16. The thin film transistor of claim 15, further comprising a source/drain electrode which is formed so that it is connected with a portion out of the channel regions in the multi-semiconductor layer.
 17. The thin film transistor of claim 15, wherein the high-angle grain boundary exists in the semiconductor layer.
 18. The thin film transistor of claim 17, wherein the high-angle grain boundary exists in the connection parts.
 19. The thin film transistor of claim of claim 14, wherein the gate electrode is equipped with one or more slots intersecting with the semiconductor layer.
 20. The thin film transistor of claim 19, wherein the semiconductor layer has the high-angle grain boundary at parts corresponding to the slots of the gate electrode.
 21. The thin film transistor of claim 15, wherein the connection parts are different layers from the semiconductor layers.
 22. The thin film transistor of claim 21, wherein the connection part is one of the same material of the gate electrode and the same material of a source/drain electrode.
 23. The thin film transistor of claim 21, wherein the high-angle grain boundary does not exist in the semiconductor layer.
 24. A thin film transistor comprising: a semiconductor layer formed in a rectangular shape having one side open or formed in a zigzag shape on an insulating substrate; and a gate electrode having at least one slot crossing the semiconductor layer; wherein the semiconductor layer has a high-angle grain boundary at a part corresponding to the slot of the gate electrode; wherein the semiconductor layer comprises: two or more body parts intersecting with the gate electrode, and one or more connection parts to connect the neighboring body parts, wherein channel regions are formed where the body parts intersect with the gate electrode; and wherein multiple gates are formed on the gate electrode, corresponding to the channel regions formed on the semiconductor layer. 